Ultrasonic switch for high speed electrical switching



Oct.8,1968 I D. moUeHENouR ETAL 3,405,246

ULTRASONIC SWITCH FOR HIGH SPEED ELECTRICAL SWITCHING Filed Aug. 26, 1966 5/6/1/4L g 58 I L.- k 46 1 E 60 aqua/v0 o 5 4 4/ .54

wa z b z ATTORNEYS Un ted St tes. Paten This invention relates to switching apparatus and more particularly to an electric switch which is adapted to operate at ultrasonic frequencies for high speed switching of electrical energy. 1

It is an object of the present invention, therefore, to provide an improved electricalswitch which is adapted t operate at relatively high frequencies.

It is also another object of the present-invention to provide a narrow bandwidth electrical switch capable of switching electrical current at extremely high speeds while operating in the ultrasonic region of the frequency spectrum. I I

It is yet another object of the present invention to provide an ultrasonicswitch which is. capable of providing switching times in the order .of millimicroseconds.

It is still another object of the present invention to provide a switch which is adapted tooperate at ultrasonic frequencies while also reducing contact bounceto a minimum.

Briefly, the subject inventioncomprises a switching arrangement having an ultrasonic piezoelectric transducer adapted to be drivenfrom an electronic driversource coupling an electrical signal thereto for causing the transducer to vibrate mechanicallyat anultrasonicrate. Mechanically coupled to the piezoelectric ultrasonic transducer is a vibrationrnagnifier which is comprised of a metallic horn configuration having a cross section which decreases from the base end connected to the transducer to the opposite or tip end. The tip end of the magnifier moreover is adapted to include a first electrical contact surface. A fixed electrical contact'having a second electrical contact surface is mounted in a fixed position adjacent the tip end of the magnifier such that the vibration imparted thereto by means of the piezoelectric transducer causes the first and second electrical contact surface to make andbreak at the frequency of vibration. Also electrical means are included for coupling a source of electrical energy across said firstand said second electrical contact surfaces. A

Other objects and advantages will become apparent as the following detailed specification is studied in conjunction with the accompanying drawing in which: FIGURE 1 is a side elevation-a1 view of a physical embodiment of the subject invention including a schematic diagram of electricaleler'nents coupled thereto;

FIGURE 2 is a schematic diagram of a circuit which is adapted to be utilized in conjunction with the embodiment shown in FIGURE lgand t FIGURES is-a diagram of waveforms illustrative of the operation of the embodiment shown'in FIGURE 1 when utilized with the circuit shown in FIGURE 2.

Directing attention now to FIGURE 1, there'is shown a housing 10 in which a piezoelectric ultrasonic transducer 12 andxa vibration magnifier 14 are mounted by means of the supporting mounts 16. The piezoelectric ultrasonic transducer 12 moreover is preferably a cylindrical element of piezoelectric material, e.g., lead zirconate titanate, barium titanate, quartz or Rochelle salt, having a predetermined length depending upon the desired frequency of operation. It is well known to those skilled in the art that when an electrical potential is applied in a. selected manner to cylindrical element, the transducer will vibrate along the axis of the cylinder, producing a 3,405,246 Patented Oct. 8, 1968 mechanical longitudinal displacement. In the subject invention, an alternating current driving source 18 is coupled across the outside and inside surfaces of the cylindrical transducer 12 intermediate the ends thereof by means of the leads 20 and 22. Electrical couplings 24 and 26 are mounted on the housing 10 so that the leads 20 and 22 may be fed therethrough to the transducer 12. v

.For purpose of illustration assuming an operating frequency of 45 kilocycles per second (kc.), the piezoelectric transducer 12 has the following typical dimensions:

ice

Inches Length 1.3 Outer diameter 6 Inner diameter A As has been stated, the length of the piezoelectric transducer is a function of the desired operating frequency. More particularly, the length of the transducer '12 is inversely proportional to the operating frequency.

The vibration magnifier 14 is physically attached to the piezoelectric transducer by means of an epoxy bond 28. The vibration magnifier moreover is preferably made out of metal which is a good conductor of electricity and has a configuration of a stepped horn of predetermined length. More particularly, the vibration magnifier 14 has a circular cross section, the diameter of which varies from one end to the other. The base end attached to the piezoelectric transducer 12 is of substantially the same diameter as the outer diameter of the transducer; however, the diameter is abruptly reduced at approximately one-half of its length to a diameter substantially smaller than the aforementioned diameter corresponding to the ouside di ameter of the transducer. The abrupt change in diameter is also adapted to coincide with one end of the housing 10. The tip end of the vibration magnifier 14 includes an electric contact surface 30. An electrical contact 32 is selectively connected to the vibration magnifier and is coupled to an electrical terminal 34 by means of a circuit lead 36. Since the vibration magnifier 14 is a good electrical conductor, an electrical potential applied to the contact 32 will be applied to the electrical contact surface 30.

The overall length of the vibration magnifier 14 is also dependent on the operating frequency and varies inversely with respect to frequency. Typical dimensions for a vibration magnifier 14 shown in FIGURE 1 operating at 45 kc. are:

Inches Base diameter Base length 1.1 Tip diameter /8 Tip length 1.1

A fixed electrical contact 38 having a second electrical contact surface 40 is positioned adjacent the tip end of the vibration magnifier 14 and is coupled to electrical terminal 41 by means of circuit lead 39. Contact 38, moreover, is adapted to be rigidly mounted on a supporting arm member 42 attached to the housing 10. An electrical insulating layer 44 is adapted to electrically insulate the supporting arm member 42 from the supporting mount 16.

In operation, when a driving signal, for example 45 kc., is coupled to the piezoelectric transducer 12 from the driver source 18, the transducer will vibrate longitudinally along its center axis at a 45 kc. rate. The mechanical vibration is coupled to the vibration magnifier 14 causing the tip to correspondingly move horizontally back and forth at a frequency of 45 kc. The subject invention utilizes the motion of the vibration magnifier 14 to act as the moving contact of an electrical switch with the fixed contact 38 being spaced a predetermined distance away from the tip end of the vibration magnifier 14 such that the first electrical contact surface 30 and the second electrical contact surface 40 will make and break at a rate equal to the operating frequency of the apparatus as determined by the frequency'of the driving signal from the alternating current source 18. The spacing between the fixed contact surface 40 and the moving contact surface is dependent on the operating frequency and is inversely proportional to the operating frequency. For example, at 45 kc., a .0015 inch maximum separation is provided; however, at 60 kc., a .0011 inch maximum separation is required. It has been observed moreover that the contacts can be closed than the aforementioned maximum separation but never farther apart for these frequencies for the configuration as disclosed in FIGURE 1.

It is essential that the fixed contact 38 be of substantial mass and mounted so as to prevent it from oscillating as a single body. Accordingly, then, the supporting arm member 42 must be of sulficient mass so as to be unaffected by the vibratory motion produced by the piezoelectric transducer 12 and magnified by the vibration magnifier 14. The supporting mounts 16 are adapted to allow the transducer-magnifier combination to vibrate freely.

When a source of electrical energy, for example the DC battery 46, is connected to one terminal 34 and output terminals 50 and 52 are adapted to be connected to the other side of the battery 46 and to terminal 41, respectively, the battery voltage will appear across the output terminals 50 and 52 in accordance with the making and breaking of the switch contact surfaces 30 and occurring when the tip of the vibration magnifier 14 makes and breaks contact with the fixed switch contact 38.

It has been observed that the rise time of the pulse generated by the opening and closing of the switch contacts is in the order of fractions of nano-seconds (l0 seconds). This Was observed by observing the waveform of the voltage appearing across the load impedance 48 when coupled to the terminals 50 and 52. A unique feature of the switch configuration comprising the subject invention is that the contact bounce inherently associated with electrical contacts making and breaking at a rapid rate is substantially reduced when considered in light of prior art switching apparatus such as relays and the like.

It is noteworthy to point out that a switch configuration as shown in the embodiment of FIGURE 1 exhibits a narrow bandwidth of operation and is dependent on the frequency of the transducer unit being utilized. This exists because of the inherent narrow bandwidth of the transducer. For example, at kc., the bandwidth of the apparatus is :75 c.p.s. Hence, switching operation occurs only if the frequency of the driving signal of the transducer is tuned within :75 c.p.s. of 45 kc. The present invention, then, combined the speeds of ultrasonic transducers with the sharp rise time of mechanical switches, while at the same time substantially eliminating the contact' bounce.

Although the vibration magnifier 14 has been described as having been comprised of metal, when desirable, other materials could be used as long as the materials utilized are not acoustically lossy materials. For example, glass and some ceramics have acoustic transmission properties. Most are, however, electrically non-conductive. In the event that the vibration magnifier is comprised of an electrically non-conductive material, an electrical contact would have to be fastened to the tip end for providing the electrical contact surface presently shown as being included as part of the metal vibration magnifier.

The subject invention can be utilized as a pulse generator when coupled to circuitry such as that shown in FIG- URE 2. Considering FIGURE 2, when using an oscilloscope, not shown, as a measuring device, the battery 46 has one terminal thereof connected to resistor 54 which is coupled to terminal 34. The opposite terminal of the battery 46 is coupled to an output terminal 50 which is adapted to be coupled to the input terminal of an oscilr: 4; F loscope. The other output terminal 52 is adapted to be coupled to oscilloscope ground. Coupled across terminals 50 and 34 is a capacitor 56. The resistance-capacitor combination of resistor 54 and capacitor 56 comprises a charging circuit for the capacitor from the battery 46. When coupled to the present invention,;closing of the switch contact surfaces 30 and 40 causes the capacitor 56 to discharge through the resistor 58 for the period of time that the switch is closed.

The waveforms shown in FIGURE 3 are illustrative of the operation of the circuitry shown in FIGURE 2 as observed across output terminals 50 and 52. At t the tip of the vibration magnifier 14 moves to the fixed contact 38 and electrical contact surfaces 30 and 40 make contact, the switch is closed and the voltage across terminals 50 and 52 goes from zero to the battery voltage in time T being in the order of fractions of nano-seconds. While the switch is closed, the capacitor 56 begins discharging through resistor 58 until the switch opens at time T During time between T and T the output voltage falls to zero and the capacitor 56 recharges to the battery potential through resistor 54.

What has been shown and described therefore is an ultrasonic switch capable of switching electrical currents at rates considerably faster than standard relays and having comparatively faster rise times with the added advantage of having comparatively little contact bounce associated therewith.

While there has been shown and described what is considered at present to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. For example, when desirable the switching contacts could be enclosed in a vacuum by a suitable enclosure which is attached so as not to dampen the vibrations. Such an embodiment would substantially increase the maximum voltage which could be switched. It is not desired, therefore, that the invention be limited to those specific arrangements shown and described but it is to be understood that all equivalents, alterations, and modifications within the spirit and scope of the invention herein are meant to be included.

We claim as our invention:

1. An electronic switch for electrical energy comprising in combination: ultrasonic transducer means responsive to an electrical driving signal for producing a mechanical vibration in accordance with said driving signal; first circuit means coupled to said transducer means for applying said driving signal thereto; vibration magnification means connected to said transducer means including a first electrical contact surface; electrical contact means including a second electrical contact surface mounted in fixed positional relationship adjacent said first electrical contact surface and cooperating therewith for making and breaking contact at a frequency substantially equal to the frequency of said mechanical vibration, said first and said second contact surface being separated a predetermined distance which is a function of said frequency of mechanical vibration; and second circuit means coupled to said first and said second contact surface for coupling a soure of electrical energy thereacross.

2. Apparatus as defined in claim 1, wherein said ultrasonic transducer means comprises a piezoelectric device having a length dimension which is inversely proportional to the frequency of said mechanical vibration.

3. Apparatus as defined in claim 1, wherein said ultrasonic transducer means comprises a cylindrical piezoelectric transducer of predetermined length, said length being a function of the frequency of said mechanical vibration.

4. Apparatus as defined in claim 3, wherein said first circuit means includes means for being coupled intermediate the length of said cylindrical piezoelectric transducer for applying said driving signal transverse to said length to produce mechanical vibration in a direction coextensive with said length.

5. Apparatus as defined in claim 1, wherein said S ii rl t Q a fiat. s at qti pri s .t :P acoustically transmissive material having a base end'which is larger in size than the opposite end and includingineans for connecting saidbase end to said ultrasonic transducer means. p

6. Apparatus as defined in claim '5, wherein said vibration magnification means. has across section which is abruptly reduced intermediate th'e'ends thereofi 7. Appanatus as defined in claim 1, wherein said vibration'niagnification means comprises a metalli'c'horn having a base end andati p end, said base end being connected to said transducer means and said tip end including said first electrical contact surface.

8. Apparatus as defined in claim 1, additionally including a housing for mounting said ultrasonic transducer means and said vibration magnification means therein.

9. Apparatus as defined in claim 8, including means connected to said housing for mounting and securing said electrical contact means thereto including means for being electrically insulated therefrom.

10. Apparatus as defined in claim 1, wherein said ultrasoriic transducer means comprises a cylindrical piezoelectric'element adapted to be energized to vibrate along its UNITED STATES PATENTS 2,497,108 2/1950 Williams 200181 XR 2,714,642 8/1955 Kinsley 200-181 2,883,486 4/1959 Mason 200181 ROBERT K. SCHAEFER. Primarv Examiner.

H. BURKS, Assistant Examiner. 

1. AN ELECTRONIC SWITCH FOR ELECTRICAL ENERGY COMPRISING IN COMBINATION: ULTRASONIC TRANSDUCER MEANS RESPONSIVE TO AN ELECTRICAL DRIVING SIGNAL FOR PRODUCING A MECHANICAL VIBRATION IN ACCORDANCE WITH SAID DRIVING SIGNAL; FIRST CIRCUIT MEANS COUPLED TO SAID TRANSDUCER MEANS FOR APPLYING SAID DRIVING SIGNAL THERETO; VIBRATION MAGNIFICATION MEANS CONNECTED TO SAID TRANSDUCER MEANS INCLUDING A FIRST ELECTRICAL CONTACT SURFACE; ELECTRICAL CONTACT MEANS INCLUDING A SECOND ELECTRICAL CONTACT SURFACE MOUNTED IN FIXED POSITIONAL RELATIONSHIP ADJACENT SAID FIRST ELECTRICAL CONTACT SURFACE AND COOPERATING THEREWITH FOR 